Compound for treatment of cardiac arrhythmia, synthesis, and methods of use

ABSTRACT

Described is a novel compound and method, useful for treatment of cardiac arrhythmias, especially useful in patients with congestive heart failure (CHF). A process for synthesizing the novel compound is also described.

CROSS-REFERENCE TO A RELATED APPLICATION

This is a division of application Ser. No. 08/468,602, filed Jun. 6,1995 now U.S. Pat. No. 5,849,788; which is a division of applicationSer. No. 08/260,869, filed Jun. 16, 1994 now U.S. Pat. No. 5,440,054;which is a continuation-in-part of application Ser. No. 08/078,371,filed Jun. 16, 1993, now U.S. Pat. No. 5,364,880.

BACKGROUND OF THE INVENTION

Congestive heart failure (CHF) is a disease affecting approximately 2%of the population of the United States (Sami, M. H. [1991] J. Clin.Pharmacol. 31:1081). Despite advances in the diagnosis and treatment ofCHF, the prognosis remains poor with a 5-year mortality rate higher than50% from the time of diagnosis (McFate Smith, W. [1985] Am. J. Cardiol.55:3A; McKee, P. A., W. P. Castelli, P. M. McNamara, W. B. Kannel [1971]N. Engl. J. Med. 285:1441). In patients with CHF, the rate of survivalis lowest in those patients with severe depression of left ventricularfunction and patients who have frequent ventricular arrhythmias.Patients with ventricular arrhythmias and ischemic cardiomyopathy havean increased risk of sudden death. The presence of ventriculartachycardia in patients with severe CHF results in a three-fold increasein sudden death compared to those without tachycardia (Bigger, J. T.,Jr. [1987] Circulation 75 (suppl.IV):28). Because of the high prevalenceof sudden unexpected death in patients with CHF, there has been agrowing interest in the prognostic significance of arrhythmias in thesepatients.

Several compounds have been used in the management of cardiacarrhythmias in patients with congestive heart failure. Unfortunately,antiarrhythmic drug therapy has been disappointing. The efficacy ofantiarrhythmic drugs markedly decreases as left ventricular functiondeclines, such that only a small fraction of patients with CHF areresponsive to antiarrhythmic therapy. No antiarrhythmic drug hasprevented sudden death in patients with CHF. There is even a question ofincreased mortality associated with certain antiarrhythmic drugs (theCAST investigators [1989] N. Engl. J. Med. 321:406).

Scientists define tachycardia and ventricular fibrillation as being ofmultiple nature. It now seems clear, and is accepted in the art, thatre-entry is the underlying mechanism to most sustained arrhythmias.Prolonging ventricular repolarization as a means of preventingventricular arrhythmias has consequently received renewed attention.This points to Class-III agents as drugs of choice in the treatment ofarrhythmias. A Class-III agent, as referred to herein, is an agent whichis classified as such in the Vaughan-Williams classification ofantiarrhythmic drugs. A Class-III agent exerts its primaryantiarrhythmic activity by prolonging cardiac action potential duration(APD), and thereby the effective refractory period (ERP), with no effecton conduction. These electrophysiological changes, which are broughtabout by blockade of cardiac potassium channels, are well known in theart. Because the blockade of cardiac potassium channels is notassociated with depression of the contractile function of the heart,Class-III agents are particularly attractive for use in patients withCHF. Unfortunately, the existing Class-III agents are limited in theirutility by additional pharmacological activities, lack of good oralbioavailability, or a poor toxicity profile. The only two Class IIIagents currently marketed are bretylium (i.v. only) and amiodarone (i.v.and p.o.).

Amiodarone is an antiarrhythmic agent having vasodilator properties thatmay benefit patients with severe heart failure. Amiodarone has beenshown to improve survival of post-myocardial infarction patients withasymptomatic high-grade ventricular arrhythmias, and it provedefficacious in patients resistant to other antiarrhythmic drugs withoutimpairing left ventricular function. Cardioprotective agents and methodswhich employ amiodarone in synergistic combination with vasodilators andbeta blockers have been described for use in patients with coronaryinsufficiency (U.S. Pat. No. 5,175,187). Amiodarone has also beendescribed for reducing arrhythmias associated with CHF as used incombination with anthihypertensive agents, e.g.,(S)-1-[6-amino-2-[[hydroxy(4-phenylbutyl)phosphinyl]oxyl]-L-proline(U.S. Pat. No. 4,962,095) and zofenopril (U.S. Pat. No. 4,931,464).However, amiodarone is a difficult drug to manage because of it itsnumerous side effects, some of which are serious.

The most serious long-term toxicity of amiodarone derives from itskinetics of distribution and elimination. It is absorbed slowly, with alow bioavailability and relatively long half-life. These characteristicshave clinically important consequences, including the necessity ofgiving loading doses, a delay in the achievement of full antiarrhythmiceffects, and a protracted period of elimination of the drug after itsadministration has been discontinued.

Amiodarone also can interact negatively with numerous drugs includingaprindine, digoxin, flecainide, phenytoin, procainamide, quinidine, andwarfarin. It also has pharmacodynamic interactions with catecholamines,diltiazem, propranolol, and quinidine, resulting in alpha- andbeta-antagonism, sinus arrest and hypotension, bradycardia and sinusarrest, and torsades de pointes and ventricular tachycardias,respectively. There is also evidence that amiodarone depresses vitaminK-dependent clotting factors, thereby enhancing the anticoagulant effectof warfarin.

Numerous adverse effects limit the clinical applicability of amiodarone.Important side effects can occur including corneal microdeposits,hyperthyroidism, hypothyroidism, hepatic dysfunction, pulmonaryalveolitis, photosensitivity, dermatitis, bluish discoloration, andperipheral neuropathy.

There is no Class-III agent presently marketed that can be used safelyin patients with CHF. The cardiovascular drug market is the largest inany field of drug research, and an effective and safe Class-IIIantiarrhythmic agent useful in patients with CHF is expected to be ofsubstantial benefit. Therefore, a drug which could successfully improvethe prognosis of CHF patients, but with a safety profile much improvedover that of amiodarone, would be extremely useful and desired.

BRIEF SUMMARY OF THE INVENTION

The subject invention pertains to novel compounds, and compositionscomprising the compounds, for the treatment of cardiac arrhythmias. Thesubject invention further concerns a method of making the novelcompounds. The novel compounds are rapidly metabolized analogs ofamiodarone, having the distinct and advantageous characteristic of beingmetabolized to a less lipophilic compound. This results in an improvedsafety profile. The new compounds can have particular utility fortreating life-threatening ventricular tachyarrhythmias, especially inpatients with congestive heart failure (CHF). The product can alsoprovide effective management for ventricular arrhythmias andsupraventricular arrhythmias, including atrial fibrillation andre-entrant tachyarrhythmias involving accessory pathways.

More specifically, the novel compounds have the particular advantage ofreducing the numerous side effects observed with the drugs currentlyavailable for treatment of these cardiac arrhythmias. For example, thecompound of choice currently used for treating cardiac arrhythmias isamiodarone, which has side effects that can be serious.

Also disclosed are novel synthesis procedures for the production of thenovel compounds. One of the novel synthesis procedures essentiallyinvolves acylation of salicylaldehyde followed by cyclization and chainelongation reactions to form methyl-2-benzofuraneacetate. This compoundis reacted with p-anisoylchloride involving a Friedel-Crafts typereaction which can use SnCl₄ as a catalyst. The compound resulting fromthe Friedel-Crafts reaction is then converted from the acetate to itscarboxylic acid form. The methoxybenzoyl moiety of the compound is alsoconverted to the hydroxybenzoyl form. This is then followed byiodination and amination to yield the subject compound. The subjectcompounds can also be converted to their various salt forms. Inaddition, the ring members can be substituted, e.g., by alkylation,acylation, or amidation reactions, and the ester function can bemodified to a series of various analogs having similar therapeuticproperties.

An alternative synthesis procedure, which also uses salicylaldehyde as astarting compound, involves a cyclization step to form2-acetylbenzofuran. This compound is then converted to itsthiomorpholide derivative, which can be further converted to2-benzofurane acetic acid, which is also formed in the other describedsynthesis procedure. The synthesis procedures are identical afterformation of 2-benzofurane acetic acid.

The subject invention thus involves the innovative development of aClass-III antiarrhythmic agent having significantly lower toxicity thanany currently available compound useful in patients with congestiveheart failure (CHF).

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b show the step-wise reaction scheme which results in thesynthesis of the novel compound, methyl2-[3-(3,5-diiodo-4-diethylaminoethoxybenzoyl)benzofurane]acetate and itshydrochloride salt form.

FIG. 2 shows an alternative synthetic scheme, where 2-benzofurane aceticacid, compound 7, can be made by synthesizing 2-acetylbenzofuran 13 fromsalicylaldehyde, followed by a chain elongation procedure known as theWillgerodt-Kindlerreaction in order to make the thiomorpholidederivative 14 which is then hydrolyzed to compound 7.

FIGS. 3A-3D show the time course of the electrophysiological effects ofequimolar concentrations of compound A and amiodarone in spontaneouslybeating guinea pig hearts. FIG. 3A is the change in atrial rate versustime plots for equimolar concentrations of amiodarone (∇) and compound A(), versus a control (∘). FIG. 3B is the change in atrioventricular(AV) interval plots for equimolar concentrations of amiodarone (∇) andcompound a (), versus a control (∘). FIG. 3C is the change in QRSinterval (intraventricular conduction time) plots for equimolarconcentrations of amiodarone (∇) and compound A (), versus a control(∘). FIG. 3D is the change in QT interval (repolarization time) plotsfor equimolar concentrations of amiodarone (∇) and compound A (),versus a control (∘).

FIGS. 4A-4D show the time course of the electrophysiological effects ofequimolar concentrations of compound A and amiodarone in atrially-pacedguinea pig hearts. FIG. 4A is the change in S-H interval(atrioventricular nodal conduction time) plots for equimolarconcentrations of amiodarone () and compound A (∇), versus a control(∘). FIG. 4B is the change in HV interval (His-Purkinje conduction time)plots for equimolar concentrations of amiodarone () and compound A (∇),versus a control (∘). FIG. 4C is the change in QRS interval(intraventricular conduction time) plots for equimolar concentrations ofamiodarone () and compound A (∇), versus a control (∘). FIG. 4D is thechange in QT interval (repolarization time) plots for equimolarconcentrations of amiodarone () and compound A (∇), versus a control(∘).

FIG. 5 shows time course of the electrophysiological effects ofamiodarone (5 μM) in atrially-paced guinea pig hearts.

DETAILED DISCLOSURE OF THE INVENTION

The subject invention concerns novel compounds which can produce thedesired pharmacological properties of amiodarone but, unlike amiodarone,are susceptible to biotransformation by plasma and tissue esterases togive a carboxylic acid metabolite. Carboxylic acids can formwater-soluble salts at physiological pH, and therefore can undergo renalelimination. As a consequence, the novel compounds, exemplified hereinby compound A, can have shorter elimination half-life. Accordingly,long-term toxicity symptoms (pulmonary fibrosis, corneal microdeposits,etc.) decrease.

One novel compound of the subject invention has the chemical name methyl2-[3-(3,5-diiodo-4-diethylaminoethyoxybenzoyl)benzofurane] acetate andhas the chemical structure shown below. ##STR1##

wherein R═H, OH, NH₂, SH, halide, alkyl, O-alkyl, acyl, O-acyl, aryl,O-aryl, substituted amine, or substituted thiol.

Y═OR₁, wherein R₁ is a straight or branched chain alkyl or heteroalkylhaving 1 to 8 carbon atoms, a substituted or unsubstituted aryl orheteroaryl; or ##STR2##

wherein R₂ and R₃ are independently selected from H, alkyl orheteroalkyl of 1 to 6 carbon atoms, or wherein N is part of a cyclic orheterocyclic group, preferentially, but not limited to, morpholine,triazole, imidazole, pyrrolidine, piperazine, pyrrole, dihydropyridine,aziridine, thiazolidine, thiazoline, thiadiazolidine and X is O, S, orNH, a derivative of said compound; or a salt of said compound, orthiadiazoline.

The structure, as shown, includes an iodinated benzene ring moiety. Itwould be understood by an ordinarily skilled artisan that other halides,including fluorine, bromine, or chlorine, can be substituted for theiodine substituents. Thus, these other halogenated compounds arecontemplated to be included as part of the invention.

The novel compounds can also be provided in their salt form, preferablythe hydrochloride salt. Other salts of the novel compounds would berecognized by those of ordinary skill in the art. In addition, the ringstructure moieties of the novel compounds can be derivatized by methodsand procedures well known by those of ordinary skill in the art. Forexample, it would be well known that various R-groups can be attached tothe six-membered ring of the benzofuran moiety of the subject compound,wherein the R groups can include H, OH, NH₂, SH, halides, alkyl,O-alkyl, acyl, O-acyl, aryl, O-aryl groups, substituted amines, andsubstituted thiols. In a preferred embodiment, R is H and X is O.

The subject invention encompasses the novel compound A and compositionscomprising these compounds. The successful application of the newcompounds to the treatment of CHF is evidenced by the evaluation of thethermodynamic properties of the compound, e.g., measuring its partitioncoefficient between water and octanol, evaluation of its kinetics ofelimination by measuring its stability in buffer and in human plasma,and evaluation of its electrophysiological properties in guinea pigheart preparations. See Examples hereinbelow. More specifically, thenovel compounds can be used for treating life-threatening ventriculartachyarrhythmias, especially in patients with congestive heart failure.This product can provide effective management of not only ventriculartachyarrhythmias and less severe ventricular arrhythmias, but alsoatrial fibrillation and re-entrant tachyarrhythmias involving accessorypathways. A composition comprising a novel compound having a rapidelimination rate can offer many advantages over the currently availableantiarrhythmic agents such as amiodarone. These advantages include:

(i) a shorter onset of action,

(ii) decreased and more manageable long-term toxicity, and

(iii) lower potential for drug interactions.

In addition, the novel compounds can be included in a compositioncomprising a second active ingredient. The second active ingredient canbe useful for concurrent or synergistic treatment of arrhythmia or forthe treatment of an unrelated condition which can be present with orresult from arrhythmia or CHF.

The subject compounds have thermodynamic properties similar to those ofamiodarone, as suggested by log P measurements, but provide theadvantageous property of being rapidly metabolized in plasma to awater-soluble metabolite. More specifically, the subject compounds areClass-III agents with electronic, steric, and thermodynamic propertiescomparable to those of amiodarone, but with an enzymatically labileester group advantageously built into the structure such that the drugcan be readily hydrolyzed in plasma to a polar, water-solublemetabolite. This water-soluble metabolite can be eliminated by thekidneys. This is a definite advantage over amiodarone, which ismetabolized primarily in the liver. Under such conditions, theelimination of the novel compound A is increased and results in a morerapid dissociation of the drug from phospholipid-binding sites. Theaccumulation of the compound, which independent on the steady-statetissue concentration of the drug, and therefore on the dose, thenbecomes easily reversible. It follows that, upon discontinuation of adrug comprising one of the novel compounds, clearance from the body ismore rapid. This increased elimination makes antiarrhythmic therapyusing the subject compounds or compositions comprising the subjectcompounds easier to manage.

Following are examples which illustrate procedures, including the bestmode, for practicing the invention. These examples should be not beconstrued as limiting. All percentages are by weight and all solventmixture proportions are by volume unless otherwise noted.

EXAMPLE 1 Synthesis of the Novel Compound

The novel compounds can be synthesized according to the scheme set outin FIGS. 1A and 1B. Below, the steps of the procedure, as shown in FIGS.1A-1B, are described in detail. The primary compounds involved in thesynthesis step are numbered corresponding to the numbers provided inFIGS. 1A and 1B.

Methyl-o-formylphenoxyacetate: 2. Approximately 509 g of the startingcompound, salicylaldehyde(1) was introduced into a 4-liter Erlenmeyerflask with powdered potassium carbonate (569 g), dimethylformamide(1,000 ml), and methyl chloracetate (478 g) and mechanically stirred at65° C. for about 24 hours. The stirring was stopped and the reactionmixture cooled to 25° C. The mixture was poured into cold water (0° C.)while stirring vigorously. An oil separated that suddenly solidified.Stirring was continued for 30 minutes and the solid isolated byfiltration. The product was washed with water (2×1,000 ml) and presseddry. The product can also be dried in vacuo at 25° C. A small sample(approx. 2 g) was purified by distillation. The boiling range of theproduct is 124-128° C. at 2 mm Hg and has a melting temperature range ofabout 50.2-50.6° C.

Methyl 2-benzofuranecarboxylate: 3. The crude product 2 was placed intoa 5-liter 3-necked round-bottomed flask equipped with a mechanicalstirrer and a water trap. Toluene (1,900 ml) was added and the solutionheated at reflux temperature (111° C.) until all water had been removed.Diazabicyclounde-7-ene (DBU) (65 g) was then added and the mixture wasstirred at 111° C., without the water trap, until the starting materialwas no longer present, i.e., was not detectable by TLC monitoring. Mostof the solvent (90%) was then distilled off. The residue was cooled to25° C., and ethyl acetate (1,000 ml) was added. The mixture wastransferred to a separatory funnel and the organic solution washed with2 N HCl (2×1,000 ml), then with water (1,000 ml). Drying was done overmagnesium sulfate. The crude product (326.56 g) was a dark oil and wasused directly in the next step. A small sample was purified for thepurpose of structure elucidation: the crude material (2 g) was dissolvedin ethyl ether and washed with 1 N KOH. Drying was done over magnesiumsulfate, the material was filtered, and the solvent evaporated. The oilyresidue was crystallized from isopropanol. The melting range is 53.8-54°C.

2-Hydroxymethylbenzofuran: 4. The crude product 3 (324 g) was dissolvedin anhydrous ethyl ether. The solution was kept under inert atmosphere(nitrogen and argon) and cooled to 0° C. in an ice bath. A 1 M solutionof lithium aluminum hydride in ether (620 ml) was added dropwise, whilestirring, over a period of 1 hour. The solution was then washed with 2 NHCl (4×1,000 ml), with 2 N KOH (2×500 ml), and with water (1,000 ml).The material was dried over magnesium sulfate, filtered, and the solventevaporated. The crude product was distilled in vacuo, yieldingapproximately 155.36 g (1.05 mol). The boiling point is 110° C. at 1.5mm Hg.

2-Chloromethylbenzofuran: 5. Compound 4 (155.25 g) was dissolved inanhydrous ethyl ether (250 ml) containing dimethylformamide (1 ml). Thereaction flask was placed into an ice bath, and when the solutiontemperature was between 0° C. and 4° C., thionyl chloride (124.3 g, 76.2ml) was added dropwise, while stirring, over the period of 1 hour. Themixture was then stirred for another hour, washed with water (250 ml),3% sodium bicarbonate solution (250 ml), and with water again (250 ml).The material was dried over magnesium sulfate, filtered, and the solventevaporated. The product was distilled in vacuo, and the yield wasapproximately 117 g. The boiling point is about 78° C. at 1.5 mm Hg.

2-Cyanomethylbenzofuran: 6. Compound 5 (117 g) was added dropwise to astirring suspension of sodium cyanide (37.64 g) in dimethyl sulfoxide(100 ml). The reactor was placed from time to time into an ice bath inorder to keep the reaction temperature between 20° C. and 45° C.Addition lasted 60 minutes. The reaction mixture was stirred for another16 hours, then poured into methylene chloride (500 ml), washed withwater (500 ml, then 2×250 ml), and evaporated to dryness. A small samplewas purified on a silica gel column, eluting with dicloromethane/hexanes(50:50 v/v).

2-Benzofuraneacetic acid: 7. The crude cyanomethylbenzofuran, compound6, was stirred for 6 hours in boiling water (1,000 ml) containing sodiumhydroxide (80 g), cooled to 25° C., then washed with methylene chloride(250 ml, then 2×100 ml). The pH was brought to 2.0 with 6 N HCl. Theprecipitate was extracted with methylene chloride (200 ml, then 100 ml,then 50 ml), dried over magnesium sulfate and the solvent evaporated.The yield was approximately 72 g.

Methyl 2-benzofuraneacetate: 8. Compound 7 (72 g) was dissolved inmethanol (200 ml) and the solution saturated with dry HCl. The solutionwas refluxed for 2 hours and the solvent evaporated. The residue wasdissolved in methylene chloride (200 ml) and the solution washed with 5%sodium bicarbonate, and then with water (100 ml). The residue was driedover magnesium sulfate and the solvent was evaporated. The product wasdistilled in vacuo. The yield was approximately 67.3 g.

Methyl 2-(3-anisoylbenzofurane)acetate: 9. Compound 8 (67 g), anhydrous1,2-dichloroethane (250 ml), and p-anisoyl chloride (59.65 g) were addedin a 1,000-ml flask under inert atmosphere. The solution was cooled inan ice bath, and SnCl₄ (115 ml) was added slowly. The bath was allowedto warm up to 25° C. and the solution was then stirred for another 24hours. The solution was poured into an ice/water mixture (1,000 ml). Theorganic phase was collected, washed with 3% sodium bicarbonate (2×500ml) and with water (500 ml), and then dried over magnesium sulfate. Thesolvent was evaporated. The oily residue was stirred for 24 hours intohexane (100 ml). The product is a pale yellow powder. The yield wasapproximately 103.3 g.

2-(3-p-hydroxybenzoylbenzofurane)acetic acid: 10. Aluminum powder (45g), benzene (900 ml), and iodine crystals (345 g) were introduced in a2-liter flask with efficient reflux condenser and mechanical stirrer.The solution was placed in a water bath and stirred until most of theheat had dissipated, then stirred at reflux temperature until the redcolor of iodine disappeared (approx. 30 minutes). This mixture wascooled to 25° C. then, while stirring, compound 9 (70 g) andtetrabutylammonium iodide (0.86 g) were added. When addition wascomplete, a portion of the solvent (600 ml) was distilled away, then theremaining solution was cooled to 25° C. A portion of ice-water (700 ml)was slowly added, followed by ethyl acetate (600 ml). The resultingsuspension was filtered and the residue washed with more ethyl acetate(2×50 ml). The organic phase was washed with more water (500 ml), thenextracted with 3% sodium bicarbonate (3×1,200 ml). The combined aqueousphases were washed with ethyl acetate (200 ml). The aqueous solution wasplaced into an ice bath and ethyl acetate (250 ml) was added. Thesolution was acidified slowly using 6 N HCl while stirring. The organicphase was washed with water (200 ml), dried over magnesium sulfate,filtered, and the solvent evaporated. The yield was approximately 26 g.

2-[3-(3,5-diiodo-4-hydroxybenzoyl)benzofurane]acetic acid: 11. Compound10 (25.25 g) was dissolved in water (250 ml) containing potassiumcarbonate (23.85 g). Iodine (47.57 g) was added and the mixture wasstirred at 25° C. for 90 minutes. Two hundred milliliters of water wasadded and the solution acidified with 2 N HCl. The residue was filtered,then dissolved in ethyl acetate (500 ml), washed with water (500 ml),then with 5% sodium thiosulfate (2×500 ml), then with water (500 ml).The residue was dried over magnesium sulfate, and the yield wasapproximately 37 g.

Methyl 2-[3-(3,5-diiodo-4-hydroxybenzoyl)benzofurane]acetate: 12.Compound 11 (16.4 g) was dissolved into methanol (100 ml) andconcentrated sulfuric acid (1 ml). The solution was refluxed for 1 hour,then the solvent was evaporated. The residue was dissolved in ethylacetate (500 ml) and washed with 5% sodium bicarbonate (300 ml).Extraction was done with 0.15 N NaOH (3×150 ml). The solution wasacidified with 6 N HCl and extracted with ethyl acetate (2×150 ml). Theorganic phase was washed with 1% sodium bicarbonate (2×300 ml) and driedover magnesium sulfate. The yield was approximately 11.64 g.

Methyl 2-[3-(3,5-diiodo-4-diethylaminoethoxybenzoyl)benzofurane]acetate:A. Compound 12 (2.88 g) was dissolved in 0.1 N NaOH solution (51 ml).Methylene chloride (25 ml) is added. Benzyltriethylammonium chloride(0.114 g) and a solution of diethylaminoethyl chloride (0.96 g) inmethylene chloride (25 ml) was then added. This was stirred for 2 hoursat 25° C. The organic phase was washed with 0.1 N NaOH (50 ml), 1 N HCl(50 ml), 0.1 N NaOH (50 ml), and water (50 ml) and dried over magnesiumsulfate to yield the subject compound.

EXAMPLE 2 Alternative Synthetic Route for the Novel Compounds

An alternative synthetic scheme is shown in FIG. 2, where 2-benzofuraneacetic acid, compound 7, can be made by an alternative reaction thatinvolves synthesizing 2-acetylbenzofuran 13 from salicylaldehyde 1reacted with chloracetone, followed by a chain elongation procedureknown as the Willgerodt-Kindler reaction in order to make thethiomorpholide derivative 14 which is then hydrolyzed to compound 7. Theremainder of the synthetic scheme to the novel compound A is thenessentially identical to Example 1.

1. Acetylbenzofuran 13. Salicylaldehyde (326.7 g) is introduced into a3-liter 3-necked round-bottomed flask containing potassium carbonate(415 g) and acetone (500 ml). Chloracetone (253.6 g) is then addeddropwise, while stirring, over a period of 30 minutes, followed byaddition of another portion of acetone (500 ml). The mixture is stirredat reflux temperature for 4 hours then cooled to 25° C. and filtered.The filtrate is evaporated and gives approximately 441 g of a redcrystalline solid, 2-acetylbenzofuran 13, which is pure enough for step2, below. To verify the identify of the product, a small portion wasdistilled in vacuo (P=0.1 mm Hg) using a short path distillationapparatus, and it was determined that the pure product distills at 80°C., yielding a white crystalline solid.

2. Benzofurane acetic acid 7. The crude 2-acetylbenzofuran 13 (441 g) isdissolved in morpholine (256.35 g) in a 3-liter 3-necked round-bottomedflask. Sulfur (≈90 g) is added, and the mixture is stirred at refluxtemperature (108° C.) for 120 minutes. This reaction yields theintermediate thiomopholide derivative 14. The mixture is cooled to 25°C. Methanol (750 ml), water (500 ml) and sodium hydroxide (220 g) areadded, and the mixture is stirred at reflux temperature (80° C.) foranother 4 hours. A portion of the solvent (750 ml) is then removed bydistillation. The volume of the solution is brought to 6 liters withwater. NaOH (40 g) and activated decolorizing charcoal (5 g) are addedand the mixture is stirred at reflux temperature for 60 minutes, thenfiltered through celite. The mixture is then acidified to pH 2 with 12 NHCl, and the product is extracted with ethyl acetate. The extract isdried over sodium sulfate and evaporated, yielding approximately 289 gof a dark solid. The crude product can be used for the next step withoutfurther purification. All physical properties of this product areidentical to compound 7, and can be used in an identical manner ascompound 7 in the synthesis scheme described in Example 1, above.

EXAMPLE 3 Partition Coefficient of Novel Compounds

The thermodynamic properties of the new compound A can be evaluated bymeasuring its partition coefficient, P, between a pH 7.4 phosphatebuffer and octanol. The buffer solution and octanol are mutuallysaturated before the experiment. The test compounds can be dissolved inthe octanol:buffer mixture at such a concentration that neither phase issaturated. The volume ratio between buffer and octanol is adjusted sothat the concentration of compound in water after equilibrium ismeasureable. The mixture is shaken for 1 hour and centrifuged in orderto obtain complete separation of the two phases. The concentration oftest compound can be measured in the aqueous phase before and afterequilibrium, using a UV detection method. The partition coefficient canbe calculated using the following equation:

    P=C.sub.o /C.sub.w

where P is the partition coefficient, and C_(O) and C_(W) are theconcentrations of test compounds in octanol and in water, respectively.Since measurements take place only in aqueous buffer, the equation hasto be modified to the following, which can be used in this experiment:

    P=[(Q.sub.i =Q.sub.w)/Q.sub.w ]×V.sub.w /V.sub.o

where Q_(i) is the initial amount of test compound introduced in thebuffer:octanol mixture, Q_(w) is the amount of test compound in bufferphrase after equilibrium has been reached, and V_(w) and V_(o) are thevolumes of buffer and octanol, respectively.

EXAMPLE 4 Stability in Buffer and Metabolism Rate in Human Plasma

Analytical method. Standard HPLC techniques can be used to determine theconcentration of the drug in buffer and in human plasma using standardanalytical procedures known in the art.

Stability in buffer. A known concentration of the novel compound A canbe incubated in a pH 7.4 phosphate buffer at 37° C. Aliquots of thesolution can be taken at various recorded intervals and diluted to theappropriate concentration for injection into the HPLC system. Thehydrolysis rate constant, K, in buffer can be calculated from the plotof drug concentration vs. time.

Metabolism rate in human plasma. The same procedure as above can be usedwith human plasma instead of buffer. The rate constant in plasma can becompared to the rate constant in buffer in order to give an approximatedrate of metabolism by plasma enzymes.

EXAMPLE 5 Electrophysiological Properties in Guinea Pig Heart

Antiarrhythmic activity in guinea pig heart preparations can be testedfor the novel compound A by methods and techniques well known by thoseof ordinary skill in the art. Antiarrhythmic activity in guinea pigheart preparations is accepted in the art as a model for antiarrhythmicactivity in humans. Specifically, activity in guinea pig heartpreparations is used to show that a compound depresses the spontaneousdischarge, slows the sinus node spontaneous firing rate, prolongs theeffective refractory period (ERP), slows the intra-atrial conduction,suppresses atrial premature beats, prolongs the ventricular ERP, anddecreases ventricular excitability. Microelectrode and pacing techniquescan be used as are standard in the art. Assays to show such activity canbe conducted in the isolated, superfused guinea pig S-A node-rightatrial preparation. A full dose-response curve for compound A can becalculated in each preparation in order to demonstrate the effects ofdifferent doses on S-A node spontaneous rate, atrial action potentialduration (APD) and ERP, and on ventricular APD and ERP. The EC₅₀ (theeffective concentration that produces 50% of the maximum response), aswell as the threshold and maximum doses for the compound can bedetermined from the full dose-response curve.

The results of electrophysiological studies carried out in guinea pigisolated hearts using the subject compound, compound A, showed thatcompound A displays electrophysiological properties classicallyassociated with Class III antiarrhythmic agents. The results of thesestudies are shown in FIGS. 3-5. Compared to the known compound,amiodarone, the electrophysical effects of the subject compound showseveral advantages. For example, on an equimolar basis, theelectrophysiological effects of compound A on atrioventricularconduction, intraventricular conduction and ventricular repolarizationtimes are much greater than those of amiodarone, both in thespontaneously beating heart (see FIGS. 3A, 3C, and 3D), and in the pacedheart (see FIGS. 4A, 4C, and 4D). In addition, the effects of compound Aon atrioventricular conduction, intraventricular conduction andventricular repolarization times can be partially reversed upondiscontinuation of the drug, whereas the effects of amiodarone are notreversed and actually tend to continue to increase even afterdiscontinuation of the drug. Compound A is also able to more selectivelyincrease the time of ventricular repolarization (i.e., prolong the QTinterval) relative to the changes observed on sinotrial nodal rate andbaseline atrioventricular nodal conduction time, as compared toamiodarone (FIGS. 3A-3D).

Specifically, FIGS. 3A-3D show the time-dependent electrophysiologicaleffects of a continuous 90-minute infusion of compound A (1 μM, n=3),amiodarone (1 μM, n=3) and vehicle (control, n=3) on the spontaneouslybeating heart. Changes from baseline values of atrial rate (FIG. 3A),A-V interval (FIG. 3B), QRS interval (FIG. 3C) and QT interval (FIG.3D), respectively, are plotted as a function of time. FIG. 3A showsthat, compared to control hearts, compound A and amiodarone causedsignificant time-dependent reductions in atrial rate of similarmagnitude. In contrast, compound A and amiodarone caused only a smallprolongation of the A-V interval (FIG. 3B). The minimal effect ofcompound A and amiodarone on atrioventricular nodal conduction inspontaneously beating hearts can be at least partly explained by notingthat atrial rate modulates the effects of drugs on atrioventricularnodal conduction. That is, concomitant slowing of atrial rate willlessen the depressant effects of drugs on atrioventricular nodalconduction. For example, in paced hearts where atrial rate is keptconstant, compound A (1 μM) had a much greater effect onatrioventricular nodal conduction (FIG. 4A). Unlike the effects ofamiodarone, the actions of compound A on A-V interval were reversed upondiscontinuation of the drug infusion, hereafter referred to as washout(FIG. 3B). In addition, compound A but not amiodarone significantlyprolonged the QRS interval, i.e., slowed intraventricular conduction(FIG. 3C). During the 90-minute washout period of compound A, thiseffect of compound A was completely reversed. Likewise, althoughcompound A and amiodarone significantly increased the QT interval, theeffect of compound A to prolong the time for ventricular repolarizationwas much greater (FIG. 3D). Whereas the effect of compound A onrepolarization was partially reversed during washout, the effect ofamiodarone was not attenuated during washout. The average baselinevalues of atrial rate, A-V interval, QRS interval and QT interval were204.6±2.4, 55.0±4.0, 21.2±0.8 and 162.5±2.9, respectively. Data areshown as mean±SEM.

FIGS. 4A-4D show a series of separate experiments, the time-dependentelectrophysiological effects of a continuous 90-minute infusion ofcompound A (1 μM, n=3), amiodarone (1 μM, n=3) and vehicle (control,n=3) in guinea pig hearts paced at 200 beats per minute wasinvestigated. Changes from baseline values of S-H interval (FIG. 4A), HVinterval (FIG. 4B), QRS interval (FIG. 4C) and QT interval (FIG. 4D),respectively, are plotted as a function of time. At equimolarconcentrations, compound A depressed atrioventricular nodal conductionin paced hearts to a much greater extent than amiodarone (FIG. 4A). Theprolongation of the S-H interval caused by compound A was gradual andreached a maximum of 18 msec (i.e., a 45% increased above the baselineS-H interval) before the drug infusion was stopped. Upon washout ofcompound A, a large fraction (≈70%) of this effect was reversed. Incontrast, amiodarone had no effect on S-H interval during the period ofdrug infusion. Compound A and amiodarone had no effect on His-Purkinjeconduction times, i.e., the HV interval remained constant (FIG. 4B).Similar to its effects on S-H interval, compound A but not amiodaroneprolonged intraventricular conduction time, i.e., increased the QRSinterval (FIG. 4C). The increase in QRS interval was gradual and reacheda maximum of 13.5 msec (60% increase above baseline value) before thedrug infusion was discontinued. The effect of compound A onintraventricular conduction was completely reversed during the 90-minutewashout period. Compound A and amiodarone both significantly increasedthe QT interval. However, compound A was much more potent at prolongingthe time for ventricular repolarization than was amiodarone (FIG. 4D).Whereas the effect of compound A on repolarization was partiallyreversed during washout, the effect of amiodarone was not attenuatedduring washout. The average baseline values of S-H interval, AVinterval, QRS interval and QT interval were 40.1±9 msec, 7.8±0.6 msec,22.3±0.7 msec, and 164.0±1.7 msec, respectively. Data are shown asmean±SEM.

FIG. 5 shows a comparsion of the electrophysiological actions of anequipotent (to prolong the baseline S-H interval) concentration ofamiodarone to those effects found using 1 μM compound A. For thispurpose, a concentration of 5 μM amiodarone was selected. Whereasamiodarone (5 μM) caused a time-dependent increase in S-H, WRS and QTintervals, it had no effect on the HV interval. Of the intervalsmeasured, amiodarone (5 μM) had the greatest effect on atrioventricularconduction time. It prolonged the baseline S-H interval by 74 msec at 90min of drug infusion before the heart went into second degree AV block.This large prolongation of S-H interval was accompanied by only a 20msec increase in the QT interval. On the other hand, although compound A(1 μM) caused an increase of 18 msec in the baseline S-H interval at90-min of drug treatment (FIG. 3A), it was accompanied by an increase inthe QT interval of 28 msec (FIG. 3D). Thus, compound A, compared toamiodarone, is able to more selectively prolong the time for ventricularrepolarization without causing as much depression of atrioventricularnodal conduction. Likewise, as shown in FIG. 3A, at comparable degreesof atrial rate slowing, compound A was able to produce a much greaterincrease in the QT interval in spontaneously beating hearts (FIG. 3D).Taken together, these data show that compound A, compared to amiodarone,can prolong the ventricular repolarization time in a more selectivemanner at concentrations that would cause less slowing of atrial rateand atrioventricular nodal conduction. The latter is an important issuebecause excessive slowing of heart rate and atrioventricular nodalconduction can cause symptoms in patients.

One of the major drawbacks of amiodarone in the clinical setting is itslong half-life (>30 days), which can causes severe life-threatening sideeffects that are slow to resolve even after discontinuation of drugtherapy. The advantages of compound A over amiodarone or other currentlycaused antiarrhythmic are that it exhibits more selective antiarrhythmicaction, has a potentially shorter half-life, and has cardiac effectswhich are more easily reversed ("washed") upon cessation of drugtreatment.

EXAMPLE 6 Uses, Formulations, and Administrations

Therapeutic and prophylactic application of the subject compounds, andcompositions comprising them, can be accomplished by an suitable methodand technique presently or prospectively known to those skilled in theart. Further, the compounds of the invention have use as startingmaterials or intermediates for the preparation of other useful compoundsand compositions. The compounds of the invention are useful for variousnon-therapeutic and therapeutic purposes. It is apparent from thetesting that the compounds of the invention have effectiveantiarrhythmic activity. Specifically, they are useful in regulatingcardiac arrhythmia, including atrial fibrillation, in animals andhumans.

The administration of the subject compounds of the invention is usefulas an antiarrhythmic agent. Thus, pharmaceutical compositions containingcompounds of the invention as active ingredients are useful inprophylactic or therapeutic treatment of cardiac arrhythmias in humansor other mammals.

The dosage administered will be dependent upon the immunomodulatoryresponse desired; the type of host involved; its age, health, weight,kind of concurrent treatment, if any; frequency of treatment;therapeutic ratio and like considerations. Advantageously, dosage levelsof the administered active ingredients can be, for examples, dermal, 1to about 500 mg/kg; orally, 0.001 to 200 mg/kg; intranasal 0.01 to about100 mg/kg; and aerosol 0.01 to about 50 mg/kg of animal body weight.

Expressed in terms of concentration, the active ingredient of theinvention can be present in the new compositions for use dermally,intranasally, bronchially, intramuscularly, intravaginally,intravenously, or orally in a concentration of from about 0.01 to about50% w/w of the composition, and especially from about 0.1 to about 30%w/w of the composition. Preferably, the novel compound is present in acomposition from about 1 to about 10% and, most preferably, the novelcomposition comprises about 5% novel compound.

The compositions of the invention are advantageously used in a varietyof forms, e.g., tablets, ointments, capsules, pills, powders, aerosols,granules, and oral solutions or suspensions and the like containing theindicated suitable quantities of the active ingredient. Suchcompositions are referred to herein and in the accompanying claimsgenerically as "pharmaceutical compositions." Typically, they can be inunit dosage form, namely, in physically discrete units suitable asunitary dosages for human or animal subjects, each unit containing apredetermined quantity of active ingredient calculated to produce thedesired therapeutic or prophylactic effect in association with one ormore pharmaceutically acceptable other ingredients, e.g., diluent orcarrier.

Where the pharmaceutical compositions are aerosols, the activeingredients can be packaged in pressurized aerosol containers with apropellant, e.g., carbon dioxide, nitrogen, propane; etc. with the usualadjuvants such as cosolvents, wetting agents, etc.

Where the pharmaceutical compositions are ointments, the activeingredient can be mixed with a diluent vehicle such as cocoa butter,viscous polyethylene glycols, hydrogenated oils, and such mixtures canbe emulsified if desired.

In accordance with the invention, pharmaceutical compositions comprise,as an inactive ingredient, an effective amount of one or more non-toxic,pharmaceutically acceptable ingredient(s). Examples of such ingredientsfor use in the compositions include ethanol, dimethyl sulfoxide,glycerol, silica, alumina, starch, calcium carbonate, talc, flour, andequivalent non-toxic carriers and diluents.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication and the scope of the appended claims.

What is claimed is:
 1. A compound having the structure ##STR3## whereinR═H, OH, NH₂, SH, halide, alkyl, O-alkyl, acyl, O-acyl, aryl, O-aryl,substituted amine, or substituted thiol;Y═OR₁, wherein R₁ is a straightor branched chain alkyl or heteroalkyl having 1 to 8 carbon atoms, asubstituted or unsubstituted aryl or heteroaryl; or ##STR4## wherein R₂and R₃ are independently selected from H, alkyl or heteroalkyl of 1 to 6carbon atoms, or wherein N is part of cyclic or heterocyclic groupcomprising morpholine, triazole, imidazole, pyrrolidine, piperidine,piperazine, pyrrole, dihydropyridine, aziridine, thiazolidine,thiazoline, thiadiazolidine, or thiadiazoline; and X is S₁ or NH; aderivative of said compound; or a salt of said compound.
 2. Thecompound, according to claim 1, wherein R is H.
 3. The compound,according to claim 1, wherein the salt of said compound is selected fromthe group consisting of the hydrochloride, oxalate, and maleate salts.4. The compound, according to claim 1, wherein the salt of said compoundis the hydrochloride salt.
 5. A pharmaceutical composition for treatingcardiac arrhythmia in an animal wherein said pharmaceutical compositioncomprises a compound having the structure ##STR5## wherein R═H, OH, NH₂,SH, halide, alkyl, O-alkyl, acyl, O-acyl, aryl, O-aryl, substitutedamine, or substituted thiol.Y═OR₁, wherein R₁ is a straight or branchedchain alkyl or heteroalkyl having 1 to 8 carbon atoms, a substituted orunsubstituted aryl or heteroaryl; or ##STR6## wherein R₂ and R₃ areindependently selected from H, alkyl or heteroalkyl of 1 to 6 carbonatoms, or wherein N is part of a cyclic or heterocyclic group comprisingmorpholine, triazole, imidazole, pyrrolidine, piperidine, piperazine,pyrrole, dihydropyridine, aziridine, thiazolidine, thiazoline,thiadiazolidine, or thiadiazoline; X is S₁ or NH; a derivative of saidcompound; or a salt of said compound; and a pharmaceutically acceptablecarrier.
 6. The pharmaceutical composition, according to claim 5,wherein R is H.
 7. The pharmaceutical composition, according to claim 5,wherein the salt of said compound is selected from the group consistingof the hydrochloride, oxalate, and maleate salts.
 8. The pharmaceuticalcomposition, according to claim 7, wherein the salt of said compound isthe hydrochloride salt.
 9. The pharmaceutical composition, according toclaim 5, wherein said pharmaceutical composition comprises about 0.01%to about 50% of said compound.
 10. The pharmaceutical composition,according to claim 5, wherein said composition comprises from about 0.1%to about 30% of said compound.
 11. The pharmaceutical composition,according to claim 5, wherein said pharmaceutical composition comprisesfrom about 1% to about 10% of said compound.
 12. A method for treatingcardiac arrhythmia in an animal, wherein said method comprisesadministering an effective amount of a compound having the structure##STR7## wherein R═H, OH, NH₂, SH, halide, alkyl, O-alkyl, acyl, O-acyl,aryl, O-aryl, substituted amine, or substituted thiol.Y═OR₁, wherein R₁is a straight or branched chain alkyl or heteroalkyl having 1 to 8carbon atoms, a substituted or unsubstituted aryl or heteroaryl; or##STR8## wherein R₂ and R₃ are independently selected from H, alkyl orheteroalkyl of 1 to 6 carbon atoms, or wherein n is part of a cyclic orheterocyclic group comprising morpholine, triazole, imiadazole,pyrrolidine, piperidine, piperazine, pyrrole, dihydropyridine,aziridine, thiazolidine, thiazoline, thiadiazolidine, or thiadiazoline;and X is S₁ or NH; a derivative of said compound; or a salt of saidcompound.
 13. The method, according to claim 12, wherein R is H.
 14. Themethod, according to claim 12, wherein said composition is administeredto a mammal.
 15. The method, according to claim 14, wherein saidcomposition is administered to a human.
 16. The method, according toclaim 12, wherein said composition is administered in combination with asecond pharmaceutical composition.